Production of sodium hydroxide



Patented Aug. 15, 950

invention relates to a continuous cyclic process for the conversion ofsodium sulfate to sodium hydroxide.

The primary object of the invention is to provide an economical methodfor producing sodium hydroxide ,from Glaubers salt which is obtainedinlarge amounts as a by-product in the manufacture of artificial fibersand other shaped articles from viscose, for example, and which is oirelative unimportance commercially.

the accompanying drawings,

.Eigure 1 is a flow sheet illustrating one embodiment of the invention;and

:1 Figure- 2 is a flow sheet illustrating another embodiment of theinvention.

wwith reference more particularly to Figure 1, the hydrated sodiumsulfate is introduced into a dissolving tower 2, where it is dissolvedin water. The solution is pumped into a carbonating tower 3 in which itis carbonated and contacts ammonia-introduced from a reactor 4. Theammoniacal solution is then pumped at a controlled rate into thereactor, in which it is saturated with ammonia. In reactor 4, thefollowing reaction occurs H2COa+NHa+NH4 HCOa and the reactor containsthe ions: sodium, am-

monium, sulfate, carbonate and bicarbonate.

The ammonia saturated solution is pumped from reactor 4 through thecarbonating towers 5 and 6,

which are operated under pressure to increase the concentration ofbicarbonate ion by solution off carbon dioxide. Carbon dioxide is forcedin at the bottom of towers 5 and 6. The carbon dioxide, rising in towers5 and 6, contacts the ainmoniacal solution passing downwardlytherethi'oug hjand unites with the ammonia to form ammonium bicarbonate.Preferably, an excess of carbon dioxide is used, to avoid expulsion ofammonia, and the temperature is controlled to prevent decomposition ofthe ammonium bicarbonate. "The ammonia and carbon dioxide used for the.formation of the ammonium bicarbonate are recovered at a subsequentstage of the proce'ss and'are cycled back to the carbonating towers. By.double decomposition between the sodium sulfate'and ammoniumbicarbonate, sodium bicarbonate and ammonium sulfate are formed intowers 5 and 6. The ammonium sulfate remains in,, solution,,and theslurry containing the solid sodiumbicarbonate is discharged at thebottom oi .tower 6. ,The carbonating towers 5 and Gmay bieoi anystandard commercial type for achievinmintimate contact between adescending liquor PRODUCTION OF SODIUM HYDROXIDE William P. Dooley,Dunbar, W. Va., assignor to American Viscose Corporation, Del., acorporation of Delaware Application June 20, 1946, Serial No. 677,969 6Claims. (Cl. zsss) Wilmington,

and-an ascending vapor, and in which the pas sage of the slurry to thedischarge end of tower 6 not impeded. For example, the towers may be ofthe screen plate type in which the screen mesh is large enough for thesolid sodium bicarbonate in the descending slurry to pass through,

without blocking the screens. As will be under-,

stood by those skilled in the art, by forcing the CO2 into towers 5 andSunder pressure, and controlling the temperature in the carbonatingtowers 5 and 6, the concentration of the bicarbonate ion is increasedwith increase in the concentration of sodium bicarbonate in the liquidflowing downwardly through columns 5 and 6 until the solubility limit isexceeded and the sodium bicarbonate is precipitated. Waste gas iswithdrawn at the top of tower 3.

The sodium bicarbonate is separated from the mother liquor containingthe ammonium sulfate, as by means of filter I, the mother liquor beingcontinuously withdrawn for working up for regeneration of the ammoniaand recovery of sulfur, as will be described more in detail hereinafter.The sodium bicarbonate may be pumped into a heater 8 in which ,it isreacted either as such or after conversion to the carbonate, withcalcium oxide, in the presence of steam, at a temperature in excess ofabout 318 C., toform, by solid phase reaction, liquid sodium hydroxideand calcium carbonate, with evolution of carbon to a temperature ofabout 270 C. to 350 C., with evolution of carbondioxide, and thecarbonate may then be reacted with calcium oxide, in

aqueous medium, to precipitate calcium carbonate and form an aqueoussolution of sodium hydroxide.

In either case, the precipitated calcium carbonate is filtered oil. andis forwarded to a lime kiln ,9 where it is decomposed to calcium oxideand carbon dioxide, the calcium oxide being cycled back to heater 8 forreaction with further quantities of sodium bicarbonate or carbonate, andthe carbon dioxide being cycled back to carbonating towers 5 and 6.

rated to dryness.

Concurrently with working up of the sodium bicarbonate to sodiumhydroxide, the mother liquor remaining after separation therefrom,

The sodium hydroxide, solution may be used as such, or it may beevapo-w,

which contains ammonium sulfate and, usually, smaller quantities ofammonium bicarbonate, sodium bicarbonate and sodium sulfate, is workedup for the regeneration of ammonia and recovery of sulfur, the ammoniabeing recycled to the ammonia reactor 4 for use in saturating furtherquantities of sodium sulfate solution.

The ammonia regeneration and sulfur recovery may be effected in severalways. In accordance with the embodiment of the invention, illustrated inFigure 1, the eflluent from filter 1 is evaporated in an evaporator I0,and the resulting anhydrous material is introduced into a heater I,where it is heated, preferably at a temperature of about 2000 C., with ametallic oxide, the corresponding sulfate of which decomposes at atemperature below 1000 C., or the sulfate of which forms sulfur trioxideon heating, such as cupric or ferric oxide, to form the correspondingmetal sulfate and evolve the ammonia. The ammonia is recycled to'the'reactor 4, and the'metal sulfate calcined in a roaster f2, tore-form the metal oxide withrelease' of sulfur trioxide. The metaloxide'is discharged from the roaster and recycled to' 'lieater ii. Thesulfur trioxide may be absorbed in dilute sulfuric acid forthe-production of concentrated sulfuric acid,i'f desired. An-y sodiumsulfate and sodium carbonate remaining after heating of the evaporatedeffluent with the metal oxide are withdrawn fromheater Hand forwarded tothe dissolving column 2.

QIn' accordance With the modification of the invention'illustrated inFigure 2, the effluent from filter T is reacted, in heater [4, with theaqueous ammonium com'plexof -a metal hydroxide,-for examplecuprammoniumhydroxide, nickel ammonium hydroxide, cadmium amoniumhydroxiiie} silver ammonium hydroxide, zinc ammonium hydroxide etc, toform a solution of the metal sulfate, with evolution of ammonia. Themetal sulfate solution is evaporated in evaporator l5, and the anhydroussulfate is introduced into a roaster lfi', anddecomposed to the metaloxide and-- sulfur trioxid'e. 7 trial vessel il in which it is reactedwith water and "a portioncf-the ammonia issuing from heater l l tore-form the aqueous ammonium complex of the metal hydroxide, whichisthen introduced into heaterlli for reaction with further quantities ofefiluent from filter 1. The remaining, portion of the evolved ammonia isrecycledto'the reactor '4. g

itwi-lllbefnoted that, in carrying'out. the describedprocess, all of thereagents are recovered andreused without loss, the process beingoperatedon acontinuous cyclic basis withmarkedefficiency and-economy.No-by-product isobtained' which is not recycled for reuse. directlyin'the form obtained or after reaction with other substances. recoveredduring the process.

While I have described my process in: terms of particular steps ascarried out in the preferred practice-of the invention, it is to beunderstoodseparating the sodium "l icarbonate from the- The metal oxideis recycled 4 slurry, and converting the sodium bicarbonate to sodiumhydroxide.

2. In a process for the production of sodium hydroxide from sodiumsulfate, the steps which comprise carbonating an aqueous solution of thesodium sulfate, saturating the solution with ammonia, carbonating theammoniacal solution to produce a slurry containing 'sodium' bicarbonate,separating the sodium' bicarbonate from the slurry, heating the sodiumbicarbonate with calcium oxide in the presence of steam at a temperaturein excess of 318 C. to form, by solid phase reaction, sodium hydroxideand calcium carbonate, and leaching the reaction product with'water todissolve the sodium hydroxide and precipitate the calcium carbonate.

3. In a process for the production of sodium hydroxide from sodiumsulfate, the steps which comprise carbonating an. aqueous solution ofthe sodium sulfate, saturating the solution with ammonia, carbonatingthe ammoniacalsoluticn'to produce a slurry containing sodiumbicarbonate? separating the sodium bicarbonate from the slurry, heatingthe sodium bicarbonate to obtain sodium carbonate, and reacting thesodium-mp bonate with calcium oxide in aqueous medium, to form anaqueous solution of sodiumh'ydroxideand precipitate calcium carbonate.

4. In a process for the production of sodium hydroxide from sodiumsulfate, the'step's which comprise carbonating an aqueous solution ofthesodium sulfate, saturatingth'e carbonated-som tion with ammonia,passing-the ammoniacalsil 9"-- lution downwardly counterourrent toascending vapors of carbon dioxidewhereb-y the ammoniacal solutionis-carbonatedand a slurry containing sodium bicarbonate is produced,separatingfl'tire sodium bicarbonate from the slurry, 'andcor -f vertingthe sodium bicarbonate to sodium droxide. r a l i 5. A'cyclic processfor theproduction-of sodium" hydroxide from sodium sulfatewhichcomprises carbonating an aqueoussolution of; thesodiumsulfatasa-turating the carbonated solution with produce liquidsodium hydroxide and calcium carbonate with evolution of carbonfdlOXidB', cycling theevolved carbon dioxid'e'for carbonating furtherquantities ofthe' ammonia-saturated carbonated sodium sulfate solution,leachiiig'the" reaction product comprising liquid sodium 'hy-'" droxidewith water to dissolve the sodium hy droxide and precipitate calciumcarbonate, sep'a rating! the sodium hydroxide solution from 'the;

calcium carbonate, converting: the calcium "carjbonate by heat tocalcium oxideand carbon di" oxide, cycling the calcium oxide for use incom, verting further quantities of sodium bicarbonate to sodiumhydroxide, cycling the carbon moxie-e evolved for carbonating furtherquantities'dfthe',

ammoniacal solution, evaporating the ammonium,

sulfate-containing liquor separated from the sodium bicarbonate, heatingthe residue f of the evaporation with a metallic oxide the corresponding sulfate of which decomposes at atemper ture below 1000C. to evolveammonia-and pro duce the metal sulfate, cycling the ammoniaforsaturatingfurther quantities of-"- carbonated" sodium sulfatesolution,-heating'the-metal-"sulfateto recover the metal oxide andproduce sulfur oxide, and cycling the metal oxide for reaction withfurther quantities of the residue remaining after evaporation of theammonium sulfate containing solution separated from the sodiumbicarbonate.

6. A cyclic process for the production of sodium hydroxide from sodiumsulfate which comprises carbonating an aqueous solution of the sodiumsulfate, saturating the carbonated solution with ammonia, carbonatingthe ammoniacal solution to produce a slurry containing sodiumbicarbonate, separating the sodium bicarbonate from the slurry to obtainthe bicarbonate and a solution containing ammonium sulfate, convertingthe sodium bicarbonate by heat to sodium carbonate with evolution ofcarbon dioxide, reacting the carbonate with calcium oxide in aqueousmedium to produce an aqueous solution of sodium hydroxide andprecipitate calcium carbonate with evoluton of carbon dioxide, cyclingthe carbon dioxide for use in carbonating further quantities of theammonia-saturated carbonated sodium sulfate solution, separating thesodium hydroxide solution, converting the calcium carbonate by heat tocalcium oxide, cycling the calcium oxide for reaction with furtherquantities of sodium carbonate, evaporating the ammoniumsulfatecontaining liquor separated from the sodium bicarbonate, heatingthe residue of the evaporation with a metallic oxide the correspondingsulfate of which decomposes at a temperature below 1000 C. to evolveammonia and produce the metal sulfate, cycling the ammonia forsaturating further quantities of carbonated sodium sulfate solution,heating the metal sulfate to recover the metal oxide and produce sulfuroxide, and cycling the metal oxide for reaction with further quantitiesof the residue remaining after evaporation of the ammoniumsulfate-containing solution separated from the sodium bicarbonate.

WILLIAM P. DOOLEY.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS OTHER REFERENCES "The Alkali Industry byPartington; Baillere, Tindall and Cox, London, 1919, page 74.

Handbook of Chemistry and Physics, Chemical Rubber Publishing Co.,Cleveland, Ohio, 28th edition (1944), pp. 488-489, 380-381.

1. IN A PROCESS FOR THE PRODUCTION OF SODIUM HYDROXIDE FROM SODIUMSULFATE, THE STEPS WHICH COMPRISE CARBONATING AN AQUEOUS SOLUTION OF THESODIUM SULFATE, SATURATING THE SOLUTION WITH AMMONIA, CARBONATING THEAMMONIACAL SOLUTION TO PRODUCE A SLURRY CONTAINING SODIUM BICARBONATE,SEPARATING THE SODIUM BACARBONATE FROM THE